Automatic control for audible electronic warning system

ABSTRACT

This invention is an electronic siren producing a siren sound having a sound wave produced on a slowly rising and falling frequency. A major cycle is pulsed at intervals with variations in frequency. The variations in each major cycle represent minor cycles. The invention utilizes an electronic circuit to effect such major and minor frequency cycles with existing speaker equipment to project the sound.

United States Patent Cieslak et al.

[ June 10, 1975 [54] AUTOMATIC CONTROL FOR AUDIBLE 3,579,233 5/1971Raschkc 340/384 E ELECTRONIC WARNING SYSTEM 3,587,094 6/1971 Scott340/384 E [75] Inventors: Richard F. Cieslak, Algonquin; John 1 v.Balding, Palatine, both of I11. j y PIttSB M w n tto ,A 1,0 ann, rown, ci [73] Assignee: Industrial Electronics Service Co., & zg r [rm ramsSchaumburg, Ill.

[22] Filed: July 9, 1973 [57] ABSTRACT [21] Appl. No.: 377,644

This invention is an electronic siren producing a siren [52] U S Cl340,384 E. 340/384 R sound having a sound wave produced on a slowly ris-[51] Gosh 3/00 ing and falling frequency. A major cycle is pulsed at[58] Fie'ld 331/47 intervals with variations in frequency. Thevariations 84/124 1 in each major cycle represent minor cycles. Theinvention utilizes an electronic circuit to effect such major and minorfrequency cycles with existing [56] EEZF E SZ Q speaker equipment toproject the sound.

2,847,663 8/1958 Stoddard 340/384 E 6 Claims, 3 Drawing Figures l2 I3 l6I71 IE IS I MAJOR SHAPING ECCLES l i TIMING JORDAN AUDIO OSCILLATORNETWORK MODULATOR a SWEEP AMPLIFIER OSCILLATOR SPEAKER VARIABLE 25 /IO20 PZCZE $335K d s i l/6:1 m H'VOLTAGE SIREN oscILLA'rpR SOURCE SWITCHII SHEET PATENTEDJUH 10 1975 we 200mm z m2 E.

m w m OON ZH NI XONBFIOEIHA BACKGROUND OF THE INVENTION The presentinvention is directed to electrical sirens and particularly to sirens ofthe type which may be used with emergency vehicles.

' Sirens commonly in use on emergency vehicles are of several types,i.e., as one utilizing a slowly rising and falling sound with a singleor repetitive cycle. one using an alternating high and low frequency ofsound or one using a slowly rising and falling sound frequency withminor sound frequency variations occurring during each cycle of therising and falling sound. In the latter class of sirens, the sound hasbeen produced by mechanical means. The first two types of soundproducing sirens have heretofore been reproduced mechanically andelectronically through use of motors or electrical amplifiers but, asfar as is known, the third class has not heretofore been producedelectronically. The mechanically produced siren noise has some desirablequalities not found in electronically produced siren sounds I which maybe attributed to purely mechanical noises resulting from the soundproducing apparatus. Mechanically driven baffling is used withmechanical sirens to create a minor pulsing of the siren sound duringeach cycle of rising and falling frequency of the sound.

SUMMARY OF THE INVENTION Electronically produced siren sounds have theadvantages that sound emitting speakers of the siren may be located atvarious points in an emergency vehicle so that the sound direction maybe predetermined. Electronically produced siren noises have the furtheradvantage of utilizing combined or existing amplifying apparatus in anemergency vehicle thus reducing electrical power requirements in suchvehicles. For example, the speakers used for producing a siren sound inthe vehicle may also be used for a public address system.

OBJECTS OF THE INVENTION With the foregoing in mind, the presentinvention has for its major purposes to provide an electronicallyproduced siren sound which closely simulates the mechanically producedsiren sound above mentioned and which produces a slowly rising andfalling sound frequency with variations in the frequency during ,eachcycle of rising and falling sound, and to enable use of suchelectronically produced sound with existing speaker facilities ofemergency vehicles, while at the same time arranging simple andeffective circuits to attain these ends at relatively low cost ofmanufacture and installation.

DESCRIPTION OF THE DRAWINGS These and other purposes will appear fromtime to time in the course of the ensuing specification and claims whentaken with the accompanying drawings, in which:

FIG. 1 is a block diagram of an electronic siren system in accordancewith the present invention;

FIG. 2 is a schematic wiring diagram of the siren system showing theelectrical relationship of all of the elements indicated in FIG. 1; and

FIG. 3 is a sound wave diagram.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in the drawings, theseveral elements of the siren system include a voltage source 10. avoltage regulator 11, a major timing oscillator 12, a shaping network13, which supplies a variable pulse rate oscillator 14. A second shapingnetwork takes the frequency supplied by the oscillator 14 and suppliesit to a modulator 16, which mixes the output from the shaping network 15with the output from the shaping network 13 and supplies this mixedfrequency to a sweep oscillator 17. Oscillator 17 supplies audioamplifier 18 for a speaker 19. A switch 20 controls the siren. The sweeposcillator 17 is powered from the voltage source I1 and is controlled bya bias voltage from modulator I6.

The sound generated by this electronic system is on a rising and fallingfrequency ranging from a peak frequency to a low frequency, requiring atime interval to reach the peak frequency and approximately the sameinterval to fall back to the low frequency. This varying frequencycomprises a major cycle but is pulsed at a continuously varying rate andat peak frequency the pulse rate is at a maximum. Each pulse varies infrequency depending upon whether the major cycle is near the high or thelow end and each pulse comprises a minor cycle. This variably pulsedsound. as generated by this system, is obtained through the circuitryillustrated in more detail in FIG. 2. This sound is showndiagrammatically in FIG. 3. As an example, the basic sound may be arising and falling frequency ranging from 400 hertz to 1600 hertz. Thesound takes approximately 3 to 5 seconds to reach the peak of 1600 hertzand the same time to fall back to the minimum. This is referred toherein as a major cycle. This varying frequency is then pulsed" at acontinuously varying rate. Near or at peak frequency, the pulse rate isat a maximum (approximately 200 cpm). These pulses shall be referred toas minor cycles. Each minor pulse varies in frequency approximately toZOOHZ and in length approximately 0.3 to 0.6 seconds, depending onwhether the major cycle is near the high or low end.

The sweep oscillator varies in output frequency with the bias voltagefrom modulator 16 so that as the bias voltage increases the outputfrequency of the oscillator also increases and when the bias voltagedecreases the output frequency also decreases. The major timingoscillator 12 operates essentially like a switch, alternately turning onfor a certain time period, as for example 3 to 5 seconds and then offfor substantially the same period of time. The shaping network 13functions to change the voltage switched on and off by the oscillator 12to a slowly rising and falling voltage wave form similar to a sine wave.It converts the square wave form of approximately 3 5 seconds durationfrom oscillator 12 to a repetitive approximate sine wave ofapproximately 6 to 10 seconds duration. This voltage wave form providesa variable bias voltage for the sweep oscillator so that the output ofthe oscillator is a cyclically varying frequency of the same duration,i.e., approximately 6 to 10 seconds. This, in turn, provides acyclically varying sound in the audio speaker of the same duration asillustrated in FIG. 3. The variable pulse rate oscillator 14 is suppliedwith the alternately rising and falling voltage from the shaping network13 and varies its pulse rate proportionately, so that, as the voltageincreases, the pulse rate also increases and when the voltage decreasesthe pulse rate also decreases. This vary- 1 regulator circuit 11includes a switch 25 and, when this switch is closed, positive voltageis applied from battery to the voltage regulator circuit. The diode 26,with the condenser 27 function as a filter while the transistor 28,resistor 29, diode 30 and condenser 31 function as a series regulator.Two D.C. supply voltages are made available from this voltage regulatorcircuit. A filtered voltage supplies the amplifier 18 and a transistoramplifier supply in shaping network 13 for modulator l6 and variablepulse rate oscillator 14. The regulated voltage provides power foroscillator 12, variable rate oscillator l4 and sweep oscillator 17.

The major timing oscillator circuit 12 is controlled by the on-off sirenswitch 20. When this switch is closed the regulated positive voltagefrom the regulator 11 is continuously applied to the timing oscillator.The resistors 32 and 33 and the condenser 34 form a timing circuitinconjunction with the timer 35. Timer 35 is a known form of timer forperiodically discharging condenser 34. The condenser 34 is chargedthrough the resistors 32 and 33 until the regulated voltage is reachedat the connection 36 on the timer, whereupon the condenser 34 dischargesthrough the resistor 33 into the timer at connection 37 until thevoltage at the connection 36 drops to approximately one-third of theregulated voltage and at this point the condenser 34 again starts tocharge and this cycle repeats continuously so long as the siren controlswitch is closed. The output of the timer 35 at the connection 38represents a square wave form, as indicated, which switches from thehigh voltage to the low voltage, i.e., from the regulated voltage toground, through the connection 39. The square wave is of approximately 3to 5 seconds duration.

The shaping network 13 includes a diode 40, resistances 41 and 42 andthe condenser 43. When the output of the timer 35 through the connection38 is at the high, or regulated voltage, the diode 40 is biased on andthe condenser 43 charges through the parallel resistors 41 and 42. Whenthe timer output through connection 38 is at the low voltage, diode 44is biased off so that the condenser 43 discharges through the resistor42. Thus, there is provided at the base of transistor 45 a slowly risingand falling wave form wherein the duration is determined by the R-C timeconstant of the variable resistance 33 and the condenser 34 in the majortiming oscillator circuit 12. Diodes 44 and 46, and resistors 47, 48 and49, are used to provide smooth starting and termination of the risingand falling voltage. The collector of transistor 45 receives power fromthe filtered source of the regulator 11. The transistor 45 amplifies thecurrent of the rising and falling wave form and applies it to theresistor 50 of the variable pulse rate oscillator circuit 14 and to theresistor 51 of the modulator circuit 16.

I In the variable pulse rate oscillator circuit 14 a programmableunijunction transistor 60 is used. Condenser 61 is charged through theresistances 50 and 62. When charged, the voltage at the anode 63 oftransistor 60 increases until it reaches approximately of the voltage atthe gate 64of the transistor. At this point transistor 60 turns on anddischarges the condenser 61 through the cathode 65 of transistor 60 andresistor 66. As the voltage applied to the resistor 50 rises and falls,the charge time of the condenser 61 accelerates and slows down,respectively, so that the transistor 60 pulses at a varying rate. Eachtime the transistor pulses, a bistable multivibrator, comprised oftransistors 67 and 68, resistors 69, 70, 71 and 72, and condensers 73and 74, is energized. This provides a square wave of varying rate orduration at the collector of transistor 68. This wave is cyclic innature and of a much shorter time duration than the wave form fromnetwork 13. Also, the range of the variation in voltage occurring duringthe wave is much smaller than the range of voltage variation produced inthe major wave.

The shaping network 15 shapes the varying minor square wave from thetransistor 68 of the variable pulse rate oscillator circuit 14, into awave form which is similar to a triangular wave, at the junction on theresistor 75 and condenser 76 and then reduces it in amplitude through avoltage divider formed by resistors 77 and 78.

The shaped wave from the major timing oscillator circuit 12 and theshaping network 13 is applied to the resistor 51 of the modulatorcircuit 16 while the varying shaped wave from the variable pulse rateoscillator circuit 14 and shaping network 15 is applied to the cathodeof the diode 79 of the modulator circuit. The resultant wave form at thejunction of the resistor 51 and the diode 79 comprises essentially theminor varying wave from shaping network 15 imposed on the major timingwave from shaping network 13.

The mixed voltage wave form from the modulator circuit 16 is applied tothe center tap of a resistor 80 in the sweep oscillator circuit 17,where it functions as a bias voltage for the transistors 81 and 82. Theoutput of the sweep oscillator at the collector of the transistor 82increases in frequency as the bias voltage increases so that, as theslowly rising and falling variable pulsing wave form is applied to thesweep oscillator, the output frequency slowly rises and falls insynchronism with the rising and falling wave form from network 13 insynchronism with the minor wave form from shaping network 15 whilecontinuously pulsing at a varying rate. The pulses occur most rapidly atthe highest frequency and occur most slowly at the lowest frequency.

The audio frequency output of the sweep oscillator 17 is then amplifiedby means of one or more audio amplifiers-l8, the circuitry of which, asshown, is generally typical of amplifiers of this type, and used todrive one or more speakers 19 whereby to project a slowly rising andfalling variably pulsing sound continuously while turned on. Thefrequency range of the output from oscillator 17 corresponds in extentto the frequency range of the sound produced.

This electronic siren system has particular application to vehicleswhere the voltage source may be on the order of twelve volts, asprovided in the usual automotive electrical system, but the principlesof the system may be utilized with other voltages and in otherinstallations where the location may be fixed. as distinguished from amoving vehicle.

It should be understood that voltage regulator cir cuits, timingoscillator circuits, wave shaping circuits, variable pulse rateoscillator circuits. sweep oscillator circuits. and audio amplifiercircuits are known individually to the art but not in the combination orfor the purpose herein described.

FINAL SUMMARY From the foregoing, it will be seen that an electronicsiren system has been provided wherein an audio section of theelectronic circuitry produces a slowly rising and falling variablypulsed sound level in accordance with frequencies developed in a basicelectronic circuit. As the major sound frequency increases during thecycle of sound. minor variations in pitch occur. The occurrence of theseminor variations becomes more rapid as the major sound frequencyincrease and less rapid as the major sound frequency decreases. Thisprovides a simulation of the pulsing of the mechanically driven sirenswhere the pulsing is produced by mechanically driven baffling, theactuation of which reoccurs at a rate corresponding to the variablerotating speed of the siren drive.

.l claim:

1. An electronic siren including an audio speaker and an amplifier forproducing sound at continual maximum audio output from said speaker inresponse to frequency variations transmitted to said amplifier,including frequency responsive amplifying means for an audio speaker. avoltage controlled sweep oscillator circuit for supplying a variablefrequency to said amplifying means to provide frequencies distinguishedfrom ambient sounds, modulating means for supplying a variable controlvoltage to said oscillator circuit. a timing oscillator circuit, saidtiming oscillator circuit including variable and settable means forsupplying a pulsating voltage, a shaping network for changing thepulsating voltage of said oscillator circuit into a slowly rising andfalling voltage which repeats in a cyclic manner, a variable rate pulseoscillator controlled by the output of said shaping network, a secondshaping network for shaping the output of said variable rate pulseoscillator circuit means for imposing a varying cyclic voltage from saidsecond shaping network on the voltage wave form supplied by said firstshaping network in said modulating means to thereby produce a number ofperiodically rising and falling minor voltage variation on the mainvoltage wave supplied to said sweep oscillator circuit to therebyproduce an amplifier control frequency having the characteristic of acyclically recurring, slowly rising and falling main frequency of soundoccurring over a preselected interval of time and a number of rising andfalling minor frequencies occurring within said major frequencyvariation during each cycle of said main frequency while it is atmaximum continual level.

2. An electronic siren system having an audio section projecting asquare form sound wave at continual maximum audio output, electronicmeans for generating said sound wave of square form and slowly risingand falling frequency on a major cycle different from that ofpredominant ambient sound, and electronic means to pulse said majorcycle and generate minor cycles to produce variable frequencies in saidsound wave. said audio output being varied in rate and direction offrequency change represented by said minor cycles to change thefrequency rate while it is at maximum continual level whereby tosimulate a changing audio level.

3. An electronic siren system as set forth in claim 2 wherein said meansfor generating said sound wave includes an electronic circuit. and saidmeans to pulse said major cycle includes a variable rate pulseoscillator in said circuit.

4. An electronic siren system as set forth in claim 3 wherein saidelectronic circuit includes a shaping network imposed on said majorcycle, and a shaping metwork imposed on said minor cycles.

5. An electronic siren system as set forth in claim 3 wherein saidelectronic circuit includes a timing oscillator for applying a variablefrequency to said sound wave.

6. An electronic siren system as set forth in claim 5 wherein saidelectronic circuit includes a shaping network imposed on said majorcycle, and a shaping network imposed on said minor cycles.

1. An electronic siren including an audio speaker and an amplifier forproducing sound at continual maximum audio output from said speaker inresponse to frequency variations transmitted to said amplifier,including frequency respOnsive amplifying means for an audio speaker, avoltage controlled sweep oscillator circuit for supplying a variablefrequency to said amplifying means to provide frequencies distinguishedfrom ambient sounds, modulating means for supplying a variable controlvoltage to said oscillator circuit, a timing oscillator circuit, saidtiming oscillator circuit including variable and settable means forsupplying a pulsating voltage, a shaping network for changing thepulsating voltage of said oscillator circuit into a slowly rising andfalling voltage which repeats in a cyclic manner, a variable rate pulseoscillator controlled by the output of said shaping network, a secondshaping network for shaping the output of said variable rate pulseoscillator circuit means for imposing a varying cyclic voltage from saidsecond shaping network on the voltage wave form supplied by said firstshaping network in said modulating means to thereby produce a number ofperiodically rising and falling minor voltage variation on the mainvoltage wave supplied to said sweep oscillator circuit to therebyproduce an amplifier control frequency having the characteristic of acyclically recurring, slowly rising and falling main frequency of soundoccurring over a preselected interval of time and a number of rising andfalling minor frequencies occurring within said major frequencyvariation during each cycle of said main frequency while it is atmaximum continual level.
 2. An electronic siren system having an audiosection projecting a square form sound wave at continual maximum audiooutput, electronic means for generating said sound wave of square formand slowly rising and falling frequency on a major cycle different fromthat of predominant ambient sound, and electronic means to pulse saidmajor cycle and generate minor cycles to produce variable frequencies insaid sound wave, said audio output being varied in rate and direction offrequency change represented by said minor cycles to change thefrequency rate while it is at maximum continual level whereby tosimulate a changing audio level.
 3. An electronic siren system as setforth in claim 2 wherein said means for generating said sound waveincludes an electronic circuit, and said means to pulse said major cycleincludes a variable rate pulse oscillator in said circuit.
 4. Anelectronic siren system as set forth in claim 3 wherein said electroniccircuit includes a shaping network imposed on said major cycle, and ashaping metwork imposed on said minor cycles.
 5. An electronic sirensystem as set forth in claim 3 wherein said electronic circuit includesa timing oscillator for applying a variable frequency to said soundwave.
 6. An electronic siren system as set forth in claim 5 wherein saidelectronic circuit includes a shaping network imposed on said majorcycle, and a shaping network imposed on said minor cycles.